LEDs having a relatively longer lifetime and lower power consumption have been used for vehicular lamps such as headlamps, instead of conventional halogen lamps having a filament. The degree of light emission, that is, the brightness of an LED depends on the magnitude of current flowing in the LED. Therefore, a lighting circuit is needed for adjusting the current flowing in the LED when the LED is used as a light source. Such a lighting circuit is normally provided with an error amplifier and conducts a feedback control so as to make the current flowing in the LED constant.
In Japanese Patent Application Laid-Open No. 2011-192865, the present inventors have proposed a technique in which an array of LEDs is employed as a light source and each LED is individually turned ON and OFF in order to make a light distribution of a headlight variable to conduct a precise light distribution control. In the lighting circuit described in Japanese Patent Application Laid-Open No. 2011-192865, a bypass switch is disposed in parallel to each of the LEDs and the bypass switch is turned ON/OFF to realize an individual turning ON/OFF of the LED.
However, in the bypass method described in Japanese Patent Application Laid-Open No. 2011-192865, the load varies at the time of switching ON/OFF of the respective bypass switches. As a result, a response speed of a driving circuit which generates a current to be supplied to the LED may cause the current to deviate from a target value in accordance with the variation in load.
Such a deviation of current from a target value, which is a problem to be solved, is not limited to the bypass method and may also occur in any light source control device having a load variation.
The present disclosure has been made in an effort to solve the problems, and intends to provide a light source control device having a good response characteristic with respect to a load variation.